The invention relates generally to a method and system for inspection of heat exchanger tubes using long-range guided-wave inspection techniques, and more particularly to a method using torsional guided waves for quickly inspecting heat exchanger tubes from the inside diameter of a tube.
Heat exchangers are used extensively in processing plants such as refineries, chemical plants and electric generation facilities, and typically comprise a multiplicity of heat exchanger tubes supported in a fixed position by a tube sheet. Each heat exchanger tube is accessible from one end for inspection and maintenance purposes. The heat exchanger tubes carry a first liquid or gas at a first temperature and are surrounded by a second liquid or gas at a second temperature, whereby heat is transferred from the first liquid or gas to the second liquid or gas, or visa-versa. In order to minimize forced shutdowns of equipment and processes due to heat exchanger failures and associated operating and maintenance costs, heat exchanger tubes are inspected on a regular basis. Since heat exchanger tubes are bundled in close proximity, making it difficult to inspect them from their outer diameter, inspections of heater exchanger tubes are conducted from the inside diameter of the tube. Because of the large number of heat exchanger tubes in a heat exchanger and the high cost of inspection, heat exchanger tubes are generally maintained based on sampled inspection data from a small number of tubes. This current maintenance practice does not result in high reliability of heat exchangers.
There have been a number of past efforts to find solutions for inspecting heat exchanger tubes. Many of these efforts have relied on inducing guided waves in the heat exchanger tube walls and detecting induced guided wave signals reflected from defects in the tube walls. Some of these solutions provided a means for inspecting a long length of tubing from a fixed probe location on the outside diameter of tubes for detection of reflected guided wave signals. The difficulty in accessing the outside diameter of heat exchanger tubes has rendered this approach impracticable. However, these methods have provided recognition that a potential solution for quickly surveying heat exchanger tube integrity, provided that the guided waves could be launched and detected from the inside diameter of the heat exchanger tubes. Because of various shortcomings of solutions disclosed in the prior art, including poor efficiency, poor defect detection capability and mode control difficulties, these solutions have not been widely accepted for practical heat exchanger tube inspections in the field.
There is a need for a nondestructive testing method in processing industries for enhancing reliability and reducing costs by quickly surveying all heat exchanger tubes in a heat exchanger and providing data suitable for determining appropriate subsequent inspection and maintenance actions. A desirable technique is one that can be applied from an inside diameter of a heat exchanger tube, can quickly inspect the entire length of a tube from one end, and requires cleaning only in an area of probe placement.